|Publication number||US4078858 A|
|Application number||US 05/754,222|
|Publication date||Mar 14, 1978|
|Filing date||Dec 27, 1976|
|Priority date||Dec 30, 1975|
|Also published as||DE2600604A1, DE2600604C2|
|Publication number||05754222, 754222, US 4078858 A, US 4078858A, US-A-4078858, US4078858 A, US4078858A|
|Original Assignee||Gretag Aktiengesellschaft|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (3), Referenced by (15), Classifications (7)|
|External Links: USPTO, USPTO Assignment, Espacenet|
The invention relates to a measuring head for determining the optical diffuse reflection properties of an object.
Determinations of the optical reflected diffusion properties of surfaces can of course provide predictable results only when carried out to specific standards. US Standard PH 2.17-1958 is one such standard. One of its requirements is that the object or target should be illuminated by a beam having an angular size of 10° and incident normal to the target surface and that only the light which is diffusely reflected over an angle of 45° ± 5° to the input slot shouldbe examined. Reversibility is permitted but has a less favourable energy balance and is therefore less suitable, more particularly in cases where only relatively weak light sources are available.
In one known measuring head comprising projection optics for illuminating the measured object or target and collecting optics having a silvered ring for the light diffusely reflected by the target at a predetermined angle to the optical axis of the projection optics the ring takes the form of a simple conical silvered mirror which projects light diffusely reflected by the target on the entry aperture of a photomultiplier. Unfortunately conical mirrors suffer from spherical aberration, with the result that the usually very small spot of the target cannot be imaged on a comparably small surface. In practice therefore it is necessary to use photomultipliers for photoelectric measurement of the diffusely reflected light, for only photomultipliers have a large enough light entry aperture or a large enough light-sensitive surface plus adequate sensitivity but they are expensive.
Apart from some special purposes, photomultipliers are being used less and less; their places being taken more and more by semiconductor photoelectric converters such as silicon planar diodes, because of their cheapness and because they are simple and easy to use. However, since large size semiconductor elements are more costly, they have not yet been used, despite their great advantages, for diffuse reflection measuring heads, at least for the kind having the beam path defined above. Of course a collecting optics systems able to cope satisfactorily with the smallness of such semiconductor elements could be devised, e.g. by means of complicated ellipsoid mirrors and/or lens systems comprising a number of lens elements, but they would be very elaborate and would reduce the cost advantage of semiconductor elements over photomultipliers.
It is therefore an object of the invention to improve the measuring head referred to above so that it can use small photo semiconductors to evaluate the diffusely reflected light.
The head according to the invention therefore employs a silvered ring which is spherical, a transparent plate disposed in the path of the beam in the collecting optics before the silvered ring, and a substantially plane silvered ring mirror and reducing optics disposed in such path after the spherical silvered mirror.
A preferred embodiment of the invention will be described in greater detail hereinafter with reference to the accompanying drawing, which is a longitudinal section through a measuring head according to the invention; merely those parts which are important to the invention being shown.
The main element of the complete system is a light tunnel or shaft 1 which is open at both its ends and which has a plane reflecting mirror 2 at its top end. A collecting lens 3 is disposed approximately at the centre of the shaft or tunnel 1. Disposed at the bottom end thereof is an annular plane parallel glass plate 4 having an annular mirror 5 vapour-coated to its underside 4'. The mirror 5 does not cover the complete under-surface of plate 4 but leaves an annular light-transmitting window 6 free.
An annular glass member 8 is mounted above the plate 4 by a spacing ring 7, and has on its underside a spherically curved concave annular surface 9 having vapour-coated thereon a ring mirror 10.
Above mirror 2 is an aplanate or rapid rectilinear lens 11 having a plane light exit surface 12 to which is secured a photoelectric converter in the form of a silicon planar diode 13.
Light emitted by a light source 14 and passing through a lens 15 to impinge on reflecting mirror 2 is reflected thereby into the shaft or tunnel 1 and concentrated by collecting lens 3 on to a measurement spot or target 16, of e.g. approximately 3 mm diameter, on a surface 17 whose diffuse reflection is required to be measured. As specified in the aforementioned U.S. Standard, the light beams 18 are incident on surface 17 at angles in the region of from 85° to 90°. Some of the light reflected diffusely by the target 16 passes through the window 6, the glass plate 4, and impinges on the spherical ring mirror or silvered ring 10, where it is reflected back through the glass plate 4 onto mirror 5 and back again through the glass plate 4 onto the aplanate 11 which projects it on the photodiode 13. The geometry of the complete system is such that the photodiode receives only light which has been diffusely reflected at angles of approximately 45° ± 5° to the surface 17.
The optics for collecting the diffusely reflected light comprises four parts -- the plane parallel glass plate 4, the spherical ring mirror 10, the plane ring mirror 5 and the aplanate 11 -- and all these items can be produced fairly simply and cheaply. The main function of the plate 4 is to remove the spherical aberration caused by the mirror 10. The plate 4 if made of ordinary glass having a refraction index of approximately 1.55 has a thickness of approximately 0.15 to 0.25 times the radius of curvature of the spherical mirror 10. Another feature which has been found to be convenient in practice is for the system to be designed so that the magnification provided by the elements 4, 10, and 5 is approximately 3 or less. This feature is directly related to the aplanate 11, since the maximum reduction which the same can provide is somewhere in the region of 3, depending upon the glass quality. Of course, the above features only relate to those cases in which the active surface of the photodiode is of approximately the same size as the illuminated area of the target. The magnification requirements are less important for relatively large photodiodes. However, since photodiodes of more than 3 mm diameter are more costly and since there are virtually no photodiodes commercially available with diameters of more than 6 mm, there are limits to the size of photodiodes which can be used.
An appropriate lens system could be used instead of the aplanate 11 and the photodiode 13 could be located at a distance from the aplanate instead of directly thereon. Nor need the glass plate 4 be plane and parallel; for instance, it could be in the form of a spherical shell. In this event, however, the shell radii should be not less than approximately 3 times the radius of curvature of the spherical ring mirror. The main factor -- applies to all the parts of the measuring head -- is easy and simple manufacture. It is not essential for the mirrors 10, 5 to be formed as vapour coatings on glass substrates. It is convenient for the plane mirror to be in optical contact with the plate 4 only if disposed on the underside thereof. Nor is the latter feature essential, but it helps to reduce the overall size of the complete measuring head. Any appropriate plastics can be used instead of glass for the various transparent items.
|Cited Patent||Filing date||Publication date||Applicant||Title|
|US3246561 *||Jul 18, 1961||Apr 19, 1966||Gen Aniline & Film Corp||Catoptric illumination means|
|US3774039 *||Mar 5, 1973||Nov 20, 1973||Scient Techn Inc||Photoelectric apparatus for detecting light reflected from an object|
|US3996476 *||Sep 10, 1975||Dec 7, 1976||Scientific Technology Incorporated||Low noise photoelectric detector apparatus|
|Citing Patent||Filing date||Publication date||Applicant||Title|
|US4275966 *||Jan 18, 1979||Jun 30, 1981||Claus Kleesattel||Method and apparatus for the measurement of hardness testing indentations|
|US4341473 *||Sep 22, 1980||Jul 27, 1982||Gretag Aktiengesellschaft||Measuring head in or for a densitometer|
|US4390280 *||Sep 25, 1980||Jun 28, 1983||Gretag Aktiengesellschaft||Illumination control for a densitometer and density measuring device having such control|
|US4865456 *||Aug 31, 1988||Sep 12, 1989||Gretag Aktiengesellschaft||Measuring head|
|US4929084 *||Jan 24, 1989||May 29, 1990||Gretag Aktiengesellschaft||Measuring head|
|US4961646 *||Jan 24, 1989||Oct 9, 1990||Gretag Aktiengesellschaft||Manual device for the detection of optical reflection properties|
|US4968140 *||Jan 24, 1989||Nov 6, 1990||Gretag Aktiengesellschaft||Manual device for the determination or measurement of photometric data using a measuring head|
|US8823944||Jan 27, 2011||Sep 2, 2014||Seiko Epson Corporation||Biological information detector, biological information measuring device, and method for designing reflecting part in biological information detector|
|US9179848||Jun 13, 2014||Nov 10, 2015||Seiko Epson Corporation||Biological information detector, biological information measuring device, and method for designing reflecting part in biological information detector|
|US9241644||Oct 22, 2014||Jan 26, 2016||Seiko Epson Corporation||Biological information detector, biological information measuring device, and method for designing reflecting part in biological information detector|
|US20110190605 *||Jan 27, 2011||Aug 4, 2011||Seiko Epson Corporation|
|DE3830732C2 *||Sep 9, 1988||May 25, 2000||Heidelberger Druckmasch Ag||Verfahren zur Feuchtmittelführung bei einer Offset-Druckmaschine|
|EP0065484A1 *||Apr 30, 1982||Nov 24, 1982||GRETAG Aktiengesellschaft||Measuring head for an apparatus measuring colour by diffuse reflection|
|EP0327499A1 *||Jan 24, 1989||Aug 9, 1989||GRETAG Aktiengesellschaft||Measuring head|
|EP2360464A1 *||Feb 2, 2011||Aug 24, 2011||Seiko Epson Corporation|
|International Classification||G01N21/47, G01D5/30, G01D5/26, G01B11/00|